Alan Turing’s Legacy Lives On

When the history books of the future are written, Alan Turing will go down in the company of Newton and Darwin and Einstein. His visions changed how humanity conceives of computation, information and pattern -- and 100 years after his birthday, and 58 years after his tragic death, Turing's legacy is alive and growing.

In celebration of his achievements, the Royal Society, the world's oldest scientific fellowship -- Newton was once its president -- published two entire journal issues devoted to Turing's ongoing influence. On the following pages, Wired looks at some of the highlights.

Above:

Turing at War

Though he hardly fit the image of a soldier, Alan Turing had the heart of one. With war on the horizon, Turing joined the British government's codebreaking office in 1938, and one year later turned the full force of his intellect on Enigma, the seemingly uncrackable German cryptography system.

"No one else was doing anything about it and I could have it to myself," he said of his decision. In a tour-de-force of logic, information theory and sheer insight, Turing designed the machines that by summer 1940 allowed Allied forces to decipher German communications. Winston Churchill would later describe it as the single largest contribution to Allied victory. Without it, the war may have had a different ending.

Photographed above is a statue of Turing in the wartime codebreaking headquarters of Bletchley Park.

The Essential Computer

Often called the father of computer science, Turing's 1936 paper "On Computable Numbers, with an Application to the Entscheidungsproblem," articulated ideas that became technological bedrock: that any computable problem could be computed on a machine, with calculations controlled by means of encoded instructions; and that code, rather than machine, was the essence of a computer.

A straightforward example of this is videogame emulation: Ambience aside, it doesn't matter if Asteroids is played on an arcade cabinet or Atari 2600 or the latest monster gaming laptop. It's just a set of instructions.

Of course, all those examples involve hardware self-evidently recognized as computers, but the concept extends to any programmable system. With the right interface, Asteroids could conceivably be played on a computer made from DNA, the design of which is now being pursued by some 60 laboratories around the world.

Patterns of the World

In the decade after World War II, Turing turned his curiosity to nature's patterns, in particular shapes and patterns in animal bodies. His hypothesized explanation dovetailed conceptually with his computational ideas of code as universal: Turing proposed that biological patterns, whatever the animal or system, emerged from a simple type of chemical interaction.

He called this a reaction-diffusion system: one chemical makes more of itself, another slows production of the first chemical, and some mechanism diffuses the chemicals across a concentration gradient. Out of this generic behavior, proposed Turing, the most fantastically complex patterns could arise.

Below, a reaction-diffusion system involving two chemicals spreading through a tray of gelatin that is slightly deeper at one end. Changes in distance from the chemicals' source and the gel's depth produce marked changes in pattern.

Citation: "Vignettes from the field of mathematical biology: the application of mathematics to biology and medicine." By J. D. Murray.
Interface Focus, 1 February 2012.

Turing Patterns for Computation

The configurations produced by reaction-diffusion systems are called Turing patterns, and in a neatly meta recursion of his thinking, they can be seen as systems of information storage suitable for use in computing.

Instead of binary ones and zeros, a chemical computer might run code based on a chemical number system, with each Turing pattern -- like those seen above in a simple experimental setup -- representing a single unit of information.

Cellular Turing

Turing proposed that reaction-diffusion systems might explain many types of cellular organization. Scientists now search for evidence of Turing's patterns in our bodies. One place they appear to exist is in stem cells that become blood vessels.

In the photograph above, blood vessel tissue structures are compared to reaction-diffusion simulation patterns. This line of research might eventually guide tissue engineering and other regenerative medicine techniques.

Turing's Wings

Many natural patterns do not arise from Turing's reaction-diffusion systems. Some are produced by what's known as morphogen-gradient reactions, in which a pattern-governing substance diffuses outwards from a single point source.

Patterns of veins on fruit fly wings, for example, are produced by morphogen-gradient reactions, a finding that originally suggested an absence of Turing patterns in insect wings. But fruit flies are very simple creatures, and more complex wings, such as those of the Orosanga japonicus moth, appear to have Turing-patterned vein structures. Turn on a porch light on a summer night and Turing's wings will be drawn to you.

In the image above, reaction-diffusion patterns are compared to O. japonicus wing veins. Below are two sets of O. japonicus wings.

A Turing Test for Free Will

One of Turing's best-known ideas is the Turing test, proposed in his 1950 paper "Computing Machinery and Intelligence" as a method of judging machine intelligence. If a computer could pass as human in conversation, wrote Turing, then for all practical purposes it could think. What occurred inside its machine mind was far less important than the outcome.

Turing was also fascinated by the nature of free will: whether it truly existed or was only an illusion disguising a deterministic universe in which events unfolded in unalterable, preordained fashion. In fact, Turing became fascinated with quantum mechanics in part because its particle indeterminacies and unpredictability suggested a basis in physics for free will.

In "A Turing Test for Free Will," mechanical engineer Seth Lloyd of the Massachusetts Institute of Technology combines these currents of Turing's thoughts. The upshot: If you believe you have free will, then you do.

Citation: "A Turing Test for Free Will." By Seth Lloyd. Philosophical Transactions of the Royal Society A, July 28, 2012.

A Lesson in Tolerance

Turing's legacy lives on in the digital world, the biological world, and perhaps at scales we're just beginning to comprehend: As seen above, the Whirlpool galaxy looks uncannily similar to cellular swirls in a slime mold. It's hard not to wonder what Turing would have accomplished had he lived. Not long before his death, he wrote to a colleague, "I'm trying to invent a new Quantum Mechanics but it won't really work. How about coming here next week and making it work for me?" -- a line delivered in jest, but no doubt containing a grain of promise.

That promise would never be realized. In mid-century Great Britain, homosexuality was a crime, and in 1952 Turing was tried and convicted in a high-profile trial. His security clearance was revoked. Given the choice between imprisonment or hormonal castration, he chose the chemicals. Publicly shamed and persecuted, this war hero and scientific titan took his own life, eating a poison-laced apple just two weeks before his 42nd birthday.

On Turing's birthday, however, let the final note be one of celebration. Below is a picture of Alan Turing drawn by his mother in 1923, a fitting tribute to all odd children who stare into flowers and see the universe.